Many patients suffer from an occasional condition of ventricular tachycardia (VT). This is particularly prevalent in patients who survive heart attacks. Generally, VT is an on-set of a condition in which the bottom chambers of the heart (ventricles) beat at a high rate. In sharp contrast to Ventricular fibrillation (VF), VT is not usually life-threatening. However, there are situation in which VT could be fatal. Generally, VT may cause fainting, loss of consciousness, anxiety and may occasionally degenerate into a fatal VF. Accordingly, while VT is not as serious as VF, it is nonetheless a condition that calls for prompt therapy and treatment.
Prior art therapy methods and devices utilize low voltage timed pulses to control VT. Some of the prior art references which teach antitachycardia pacing using low voltage shock therapy systems include U.S. Pat. No. 4,408,606, U.S. Pat. No. 4,398,536, U.S. Pat. No. 4,488,553, U.S. Pat. No. 4, 488,554, and U.S. Pat. No. 4,390,021, all assigned to Telectronics. Other patents dealing with antitachycardia pacing (ATP) include U.S. Pat. No. 4,181,133 and U.S. Pat. No. 4,280,502, assigned to Intermedics.
Generally, a limitation of the prior art is the fact that low voltage shock therapy for use in antitachycardia pacing may accelerate the VT and may transform it into a lethal VF. In an attempt to reduce this risk, it was necessary to equip patients with a separate implantable defibrillator in the event an antitachycardia pacing therapy for VT induces a VF. However, this arrangement was not only expensive but also rather bulky and inconvenient for the patient. An alternate solution has been to equip an implantable cardioverter defibrillator (ICD) with an antitachycardia pacing device. Such a configuration is disclosed in U.S. Pat. No. 4,830,006.
In spite of the many advances made by the prior art, most of the configurations and devices are cumbersome, expensive and inconvenient for the patient. Specifically, most of the devices incorporated with an ICD require a space-volume of between 60 to 100 Cubic centimeters in volume partly because of the need for large batteries and capacitors.
Accordingly, there is need for a compact antitachycardia pacemaker which is both practicable and space-volume efficient to be implanted in patients to provide specific therapy for VT.